1. Field of the Invention
This invention relates to an apparatus for lifting the top sheet of material from a stack of materials. More particularly, this invention relates to an apparatus for lifting a top sheet of material from a stack of material by use of a gas under a positive elevated pressure which gas is discharged from a central gaseous conduit in an outwardly radial direction through an arcuately or ring-shaped conduit.
2. Discussion of the Prior Art
Numerous devices have heretofore been proposed for raising the top sheet of a stack of sheets arranged in the form of a pile. Generally speaking, those devices which have heretofore been proposed have been devices which operate by the use of a negative pressure (partial vacuum) and thus aspirate or suck the top sheet upwardly. In order to raise the sheet, these partial vacuum apparatuses are positioned quite close to the front of the back edge of the sheet and grip it by means of a vacuum. The probability that, apart from the top sheet, sheets positioned directly therebelow are also raised is relatively high, especially when it is desired to raise the top sheet of a pile of sheets which is made of a porous material. In such instances the vacuum exerted against the top sheet is usually of such a magnitude that it tends to effect those sheets disposed beneath the top sheets. For this reason a series of measures has been taken, e.g., the provision of small spring brushes past which the edge of the sheet has to be guided so that a lower sheet is prevented from adhering to the top sheet.
A further proposed measure for raising a top sheet apart from sheets therebeneath has involved the blasting of the front edge of the sheet with a blast of air so that small air pockets are formed between the upper sheets. Moreover, the suckers work with strong suction air but with small diameter as it has been shown that the tendency to entrain a sheet is less when the cross section of the sucker means is small in relation to the strength of the paper.
Finally, the tilting of the top sheet by means of a sucker member has also been known. This has been provided so that the stiffness of the underlying sheet aids the raising of the top sheet. However, all of the measures heretofore proposed have not been sufficient to guarantee that only the top sheet is raised.
Apart from the suction members heretofore proposed, which without exception work by the use of negative air pressure, the raising of the top sheet by use of blast nozzles working in conjunction with suction nozzles is known. These blast nozzles have a flat front side which in turn has a blast air outlet aperture disposed in the middle thereof. In this device, the blast stream is directed against the sheet and the sheet is sucked away by laterally arranged suction nozzles operated at negative pressure. However, it is doubtful that such a device is able to raise the top sheet, apart from other sheets, without entraining sheets underlying the same. In such connection reference is made to German Auslegeschrift No. 1,060,874.
It therefore became desirable to provide a device which would guarantee that only the top sheet of a pile of sheets was raised. More particularly, it became desirable to provide an apparatus which not only would raise only a top sheet of a pile of sheets but would hold that top sheet in a raised position independent of the sheets disposed therebeneath. Finally, it became desirable to provide an apparatus for raising the top sheet of a pile of sheets which guaranteed a safe separation even when the top sheet was porous to air.